Bandwidth enhancement for transimpedance amplifiers

A technique for bandwidth enhancement of a given amplifier is presented. Adding several interstage passive matching networks enables the control of transfer function and frequency response behavior. Parasitic capacitances of cascaded gain stages are isolated from each other and absorbed into passive networks. A simplified design procedure, using well-known low-pass filter component values, is introduced. To demonstrate the feasibility of the method, a CMOS transimpedance amplifier (TIA) is implemented in a 0.18-/spl mu/m BiCMOS technology. It achieves 3 dB bandwidth of 9.2 GHz in the presence of a 0.5-pF photodiode capacitance. This corresponds to a bandwidth enhancement ratio of 2.4 over the amplifier without the additional passive networks. The transresistance gain is 54 dB/spl Omega/, while drawing 55 mA from a 2.5-V supply. The input sensitivity of the TIA is -18 dBm for a bit error rate of 10/sup -12/.     

Bandwidth enhancement of transimpedance amplifier by acapacitive-peaking design

Using a capacitive-peaking (C-peaking) technique to increase the bandwidth of a transimpedance amplifier has been proposed. An analytical model for determining the peaking capacitance in the Butterworth-type transimpedance amplifier design has been derived. Based on this approach, we can design a larger bandwidth of a transimpedance amplifier. The low-frequency transimpedance gain in our fabricated amplifier is 0,95 kΩ, and the 3 dB bandwidth of the transimpedance amplifier is enhanced from 1.1 to 2.3 GHz without sacrificing its low-frequency gain by this C-peaking technique     

Photonic bandgap fibre oscillators and amplifiers

In the search for ever higher output power or energy from fibre oscillators or amplifiers a nowadays mature technology relies on enlarging the fibre mode area. Broadening of the core diameter, all other things being equal, inevitably yields a multimode fibre, thereby dramatically limiting the device usefulness. Various strategies have been deployed to design and manufacture single transverse mode fibre oscillators and amplifiers, among which making use of the so-called photonic bandgap effect to restrict the modal population seems promising. Helped by efficient and reliable numerical tools the design of large mode area singlemode photonic bandgap fibres is presented. Two fibres with 20-μm and 40-μm core diameter, both of them heavily doped with Yb³⁺ ions, have been fabricated by the widespread modified chemical vapour deposition process and are shown to behave properly when used as the core element of either continuous wave oscillators or femtosecond amplifiers. Good output beam quality (M² parameter spanning from 1.12 to 1.5 for the set of fibres studied) and high slope efficiency of 80% in cw oscillation regime are demonstrated. Furthermore the 40-μm core diameter fibre is shown to be resilient to tight bending down to 7.5-cm radius. The stack-and-draw process makes it easy to tailor the outer cladding so that a large numerical aperture can be reached. Subsequently, from this air-clad fibre, 500 fs 47 W pulses at 35 MHz are obtained from a two-stage chirped pulse amplification system.     

Backward optical parametric oscillators and amplifiers

Degenerate backward optical parametric oscillators and amplifiers have been considered, for the first time, to the best of our knowledge. When the pump intensity is four times the threshold pump intensity, the conversion efficiency reaches a maximum value. On the other hand, for nondegenerate optical parametric oscillators, the conversion efficiency always increases as the pump intensity increases. This behavior is different from those for forward optical parametric oscillators. In either configuration, the oscillation can occur without an external feedback. There is, however, a distributed feedback provided through the opposite propagation directions of the signal and idler. The threshold pump intensities for the oscillators can be achieved by the lasers currently available based on quasi-phase matching in several structures. As the input intensity for the backward parametric wave increases, the gain for this wave decreases dramatically if the pump intensity is on the order of the threshold or higher. When the input intensity is much larger than the threshold pump intensity, there is almost no gain regardless of the level of the pump intensity     

Large-signal characteristics of InP-based heterojunction bipolartransistors and optoelectronic cascode transimpedance amplifiers

A large-signal model for InP/InGaAs-based single HBTs incorporating soft-breakdown effects to the LIBRA Gummel-Poon (GP) model is developed and its validity is established from DC to microwave frequencies and over a wide range of input excitation levels. The large-signal characteristics of a cascode InP-based transimpedance optoelectronic preamplifier employing such devices are studied. Gain compression for the preamplifier was found to take place at an input power level of -20 dBm. Input power excitation varying from -65 to -5 dBm results in a degradation of the amplifier transimpedance gain of the order of 3 dBn. Experimental and theoretical characteristics are presented for the InP-based HBTs and transimpedance amplifier. Self-biasing effects are suggested as possible origin of the transimpedance variations with input power     

Analysis and design of LC amplifiers and LC oscillators using current-feedback amplifiers

The present paper discusses specific types of LC amplifier and LC oscillator using a current-feedback amplifier (CFA). The main advantage of the CFAs versus voltage-feedback amplifiers (VFAs) is their gain-bandwidth independence. Some of the monolithic CFAs provide an additional pin between the first stage (current-controlled current source) and the second stage (voltage follower), where the resistance is very high. This allows a parallel resonance LC tank to be connected to the additional op amp correction pin. The main advantage of this new configurations is the insignificant influence of the load over the parameters of the circuit (voltage gain, Q-factor, etc.). Some recommendations for designing this kind of analogue circuit are given, based on simulation results, symbol analysis of the transfer function and physical experiments as well as elements’ values calculation using centre frequency, voltage gain, bandwidth and Q-factor of the LC amplifiers as input parameters.     

Traveling-wave amplifiers and backward-wave oscillators for VHF

An important aspect of the design of traveling-wave amplifiers and backward-wave oscillators for frequencies below 500 mc is the problem of obtaining a tube of reasonably small physical dimensions. Hollow beams of greater perveance than is obtainable with solid beams offer one method of reducing the size of such tubes by permitting operation at a lower voltage and greater gain per wavelength, for a specified beam power, than is possible in a solid beam tube. Some aspects of the design of minimum size hollow-beam forward-wave amplifiers using single helix circuits and backward-wave oscillators using bifilar helix circuits are presented. Several tubes of these types for operation below 500 mc have been built. Amplifier bandwidths and oscillator tuning ranges in excess of four to one in frequency have been obtained experimentally. Amplifier efficiencies in excess of 20 per cent and oscillator efficiencies in excess of 10 per cent have been achieved.     

Analytical analysis of experimental TRAPATT amplifiers and oscillators

A method of analysis of TRAPATT amplifiers and oscillators has been developed, based upon a simple diode model and circuit impedance measurements. Calculations for fundamental and second-harmonic extraction devices are shown to be in good agreement with experimental measurements.     

Experimental characterisation of avalanche-diode reflection amplifiers and locked oscillators

Qualitative experimental results are presented for a silicon IMPATT diode on the distinction between the undercoupled quenched oscillator, optimised oscillator, locked oscillator, stable amplifier, in relation to the gain, linearity and saturation power. The results are consistent with a nonlinear interpretation of the equivalent diode conductance.     

Leakage current enhancement in impatt oscillators by photoexcitation

A technique for investigating the r?le of dynamic or effective leakage current in the r.f. performance of an impatt diode is described. The technique involves the design of a device structure and microwave cavity which permits the leakage current to be varied externally by photogeneration of carriers, and is compatible with c.w. operation. Typical results for flat-profile single-drift X-band silicon are a 10% reduction in power and a 10 MHz increase in frequency at a photo/bias-current ration of 0.005.     

On the limitations of transimpedance amplifiers as tools for low-frequency noise characterization

An experimental set-up for the characterization of low-frequency noise on two terminal devices is reported. The experimental set-up is based on the use of the commercial transimpedance amplifier (TA) EG&G5182. This paper addresses the influence of the TA on the noise characterization process by describing the TA as a non-ideal operational amplifier with a feedback resistor. The impact of the TA finite input resistance and voltage gain is highlighted through comparison with measurements carried out on resistors and diodes.     

片状放大器的应力应变

测量了片状放大器的应力、应变,改进了密封材料及安装方法,找到了一种不产生应力的密封方式.     

Influence of uniaxial tensile strain on the performance of partially depleted SOI CMOS ring oscillators

The influence of uniaxial tensile strain on the performance of advanced partially depleted silicon-on-insulator CMOS ring oscillators is reported. Strain is applied either perpendicular or parallel to the direction of current flow by bending of thinned, fully processed wafers with a gate oxide thickness of less than 1.5 nm. Interestingly, the standby power dissipation of the ring oscillators increases for both parallel and perpendicular strains due to changes in the gate tunneling currents with strain. The on-state power dissipation decreases with parallel strain and increases with perpendicular strain consistent with the expected changes in the inversion layer piezoresistance. The speed of the ring oscillators improves with perpendicular strain and degrades with parallel strain, which can also be understood in terms of the piezoresistance changes.     

Noise enhancement in laser amplifiers caused by gain nonuniformity

We have calculated the noise-enhancement factor of a semiconductor laser amplifier with a very thin active region. This (somewhat academic) model exhibits large Petermann's K-factors. However, the calculated noise-enhancement factor K? is only about half the K-value. The reason for the discrepancy is that in evaluating K? the radiation modes of the guiding structure have been taken into account. Similar conclusions have been reached for realistic laser models. These theoretical considerations show that gain-guided laser amplifiers are not as noisy as was originally thought.     

Jitter and phase noise in ring oscillators

A companion analysis of clock jitter and phase noise of single-ended and differential ring oscillators is presented. The impulse sensitivity functions are used to derive expressions for the jitter and phase noise of ring oscillators. The effect of the number of stages, power dissipation, frequency of oscillation, and short-channel effects on the jitter and phase noise of ring oscillators is analyzed. Jitter and phase noise due to substrate and supply noise is discussed, and the effect of symmetry on the upconversion of 1/f noise is demonstrated. Several new design insights are given for low jitter/phase-noise design. Good agreement between theory and measurements is observed     

Simple 1 micron ring laser oscillators pumped by fiber-coupledlaser diodes

We have designed simple nonplanar Nd:YAG ring laser oscillators that utilize all flat mirrors and are pumped by the fiber-coupled output from ten 3 watt diode lasers. We have obtained up to 8.5 W at 1.06 microns of diffraction-limited, single frequency output with no measureable astigmatism or ellipticity with a total pump power of 26 W from a pair of 400 micron diameter fibers. Convex curved surfaces on the Nd:YAG rod are used to increase the cavity mode size at the rod while minimizing the contribution of aspheric thermal lensing. Comparison to a linear cavity with no intracavity polarizing element indicates that stress depolarization is a significant loss mechanism in the ring laser. The cavity design is also suitable for use with birefringent laser media, such as Nd:YLF or Nd:YVO₄     

A note on the efficiency of reflection amplifiers and locked oscillators

The dc to RF conversion efficiency for reflection amplifiers and locked oscillators employing negative resistance devices such as transferred-electron effect and avalanche diodes is discussed. It is shown that one particular definition of efficiency is more appropriate than another definition sometimes employed.     

Eigenpolarization theory of monolithic nonplanar ring oscillators

Diode-laser-pumped monolithic nonplanar ring oscillators (NPROs) in a applied magnetic field can operate as unidirectional traveling-wave lasers. The diode laser pumping, monolithic construction, and unidirectional oscillation lead to narrow linewidth radiation. Here, a comprehensive theory of the eigenpolarizations of a monolithic NPRO is presented. It is shown how the properties of the integral optical diode that forces unidirectional operation depend on the choice of the gain medium, the applied magnetic field, the output coupler, and the geometry of the nonplanar ring light path. Using optical equivalence theorems to gain insight into the polarization characteristics of the NPRO, a strategy for designing NPROs with low thresholds and large loss nonreciprocities is given. An analysis of the eigenpolarizations for one such NPRO is presented, alternative optimization approaches are considered, and the prospects for further reducing the linewidths of these lasers are briefly discussed